Oil, petroleum products, natural gas, hazardous liquids, and the like are often transported using pipelines. The majority of these pipelines are constructed from steel pipe. Once installed, a pipeline will inevitably corrode or otherwise degrade. Proper pipeline management requires identification, monitoring, and repair of defects and vulnerabilities of the pipeline. For example, information collected about the condition of a pipeline may be used to determine safe operating pressures, facilitate repair, schedule replacement, and the like.
Typical defects of a pipeline may include corrosion, gouges, dents, and the like. Corrosion may cause pitting or general wall loss, thereby lowering the maximum operating pressure of the pipeline. Vulnerabilities may also include curvature and bending anomalies, which may lead to buckling, and combined stress and chemical or biological action such as stress corrosion cracking. Without detection and preemptive action, all such defects and vulnerabilities may lead to pipeline failure.
Information on the condition of a pipeline is often collected using an in-line inspection tool. An in-line inspection tool typically uses sensors to collect information about a pipeline as it travels therethrough. In the past, in-line inspection tools have used magnetic flux leakage to determine the condition of a pipeline wall. Flaws in ferromagnetic pipe can be detected by the perturbations they cause in a magnetic field applied to the wall of a pipeline.
To collect useful data, the sensors carried by an in-line inspection tool must closely track the interior surface of the pipe being inspected. However, the interior surfaces of pipes are not uniform and the sensors must move relative to the central parts of the inspection tool as the tool passes pipe sections with varying interior surfaces. Accordingly, the mechanisms connecting the sensors or inspection assemblies to the rest of the in-line inspection tool must accommodate this relative movement.
Various mechanisms have been designed to connect inspection assemblies to in-line inspection tools. One such design is a linkage fabricated as a parallelogram. In this design, a link at the front of the assembly is parallel to a link at the rear of the assembly, thereby allowing the assembly to move radially relative to the rest of the in-line inspection tool. These linkages are straightforward, but consume significant space as the assembly collapses on top of the rear linkage. Accordingly, they have difficulty in accommodating sharp bends in a pipeline. Furthermore, they must move parallel to their support axis and they can not conform to irregularities such as welds without lifting off from the pipe surface.
Another design is a mechanism that simply does not include a rear linkage, relying alone on a connection at the front of the assembly. These mechanisms cannot precisely control the position of the back end of the assembly. Yet another design uses a rear link mounted in a slot or slide, permitting assembly to move radially relative to the rest of the in-line inspection tool. However, the motion of this last design can be significantly hampered when debris fills the slot or slide.
In view of the foregoing, current linkages prevent rotation of inspection assemblies, allow inspection assemblies to wander away from their designated track, introduce attributes that cause the inspection assemblies to lift away from the pipe, succumb to debris, and the like. What is needed is a new mechanism for connecting inspection assemblies to an in-line inspection tool. This new mechanism must repeatably permit the necessary relative motion, while providing precise control over that motion.